In a conventional liquid crystal display device, a gradation correction is carried out by enlarging the dynamic range of the contrast of a video signal, thereby adjusting the contrast of the video signal. For example, patent literature 1 discloses a liquid crystal display device for detecting feature quantities including an average luminance, a maximum luminance and a minimum luminance from a video signal and adjusting a dynamic range, i.e. a contrast gain in accordance with the detection result.
However, in the case of changing the contrast gain in real time in accordance with changes of the feature quantities, the contrast gain frequently switches in a video signal whose brightness drastically changes and this switch is viewed as a flicker by a user, wherefore the video quality is degraded.
In order to prevent the above frequent switch, the contrast gain is switched with a certain time constant. However, even in the case of decreasing the contrast gain, the contrast gain is switched with a delay of only a period of the time constant and a state before the adjustment is kept only for the period of the time constant. Therefore, even in this case, the degradation of the video quality cannot be completely avoided.    Patent Literature 1: Japanese Patent No. 3215388